Hydrogen sulphide is a gas which is toxic, inflammable, explosive and corrosive, in particular vis-a-vis ferrous metals. Natural gases are very often contaminated by hydrogen sulphide which must be eliminated as quickly and as completely as possible before they are sent to sites for conversion or consumption. In order to do this, it was proposed to treat these gases contaminated with hydrogen sulphide either with aldehydes such as formaldehyde, acrolein, isobutyraldehyde, glyoxal, in aqueous solution or in emulsion, optionally in the presence of emulsifiers or amines such as butylamine, monoethanolamine, 4-aminoethyl 1,8-diamino octane, N,N'-dimethylethylenediamine (U.S. Pat. Nos. 1,991,765, 3,459,852, 4,501,668, 4,532,117, 4,680,127, 4,767,860, 4,978,512, 5,085,842, 5,152,916, 5,225,103, 5,223,175, European Patent Application Nos 383,499, 405,719, 411,745, 475,641, 475,642 and 540,666), or with metal oxides such as iron or zinc oxides, or with oxidizing agents such as sodium nitrite, hydrogen peroxide, sodium chlorite, chlorine dioxide (U.S. Pat. No. 4,515,759, Canadian Patent No. 1,207,269, European Patent Application Nos 082,513, 261,974 and 389,150). Although these products have useful properties for trapping hydrogen sulphide, more economical, more effective products are sought today which act more rapidly and do not produce any insoluble product.
WO-A-91 10634 describes the use of aromatic heterocyclic metal-ligand complexes to catalyze the action of the oxygen added to a medium to be treated containing hydrogen sulphide or thiols; so that the oxygen can act, it is necessary to carry out the process in an organic medium, in the presence of a cosolvent.